1. Field of the Invention
This invention relates to a fuel injection amount control apparatus that controls a fuel injection amount to be supplied to an internal combustion engine according to operating conditions. Particularly, the invention relates to a fuel injection amount control apparatus for an internal combustion engine arranged to perform OTP boosting of a fuel injection amount to prevent overheating of a catalyst or the like during high load and high rotation engine operation and to perform power boosting of a fuel injection amount to enrich an air-fuel ratio to an output air-fuel ratio during high load engine operation.
2. Description of Related Art
For control of the fuel injection amount for an internal combination engine, boosting for Over Temperature Protection (OTP) and power boosting have conventionally been applied to correct the fuel injection amount according to the operating condition of the internal combination engine. OTP boosting is generally a boost correction that is performed to prevent overheating of a catalyst or the like for detoxifying exhaust gas provided in an exhaust passage during high load and high rotation operation of the internal combustion engine. By boosting the fuel injection amount and enriching the air-fuel ratio, the OTP boosting can decrease the exhaust gas temperature and suppress a rise of the catalyst temperature. On the other hand, power boosting is generally capable of enriching the air-fuel ratio to make up for output shortage during high load operation (e.g., full-throttle acceleration) of the internal combustion engine.
A fuel injection control apparatus for an internal combustion engine, which is described, for example, in Jpn. unexamined patent publication No. 7(1995)-166918, is adapted to perform OTP boosting to prevent overheating of an exhaust system including a catalyst. This apparatus is also adapted to determine whether the catalyst is active by estimating the catalyst temperature using an integration value of intake air amount and arranged not to perform OTP boosting when the catalyst becomes not more than an active temperature at cold start or the like. This apparatus can estimate the catalyst temperature and therefore has a merit of dispensing with a catalyst temperature sensor.
On the other hand, an acceleration control apparatus, which is described, for example, in Jpn. unexamined patent publication No. 9(1997)-96234, carries out power boosting (enrich control). In particular, this apparatus is adapted to perform enrich delay control that is arranged to start enrich control for power boosting after the elapse of a certain period of time after enrich control conditions are fulfilled during acceleration of an internal combustion engine. The apparatus is also adapted to stop the enrich delay control and start enrich control, when the catalyst temperature detected by a sensor exceeds a predetermined temperature during the enrich delay control.
Here, for example, it is conceivable to control the fuel injection by combining the above-mentioned OTP boosting based on the estimated catalyst temperature with the above-mentioned power boosting during high load operation.